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Studies in animals including monkeys have shown that reducing food intake can benefit health and increase lifespan.

Researchers have found that reducing calories by as much as 30 per cent could reduce risks of developing heart disease or cancer by half and increase lifetimes by nearly a third.

The extreme diets - just above malnutrition levels - add an extra 25 years to the average life in Britain with the vast majority of people living to their 100th birthday

But in a series of new experiments on fruit flies, scientists discovered that simply varying the mix of amino acids in the diet affected lifespan.

Further study revealed that one particular amino acid, methionine, made all the difference.

Although flies and people are very different, the researchers believe the effects are likely to be conserved throughout a wide range of different species including humans.

Dr Piper said: "It's not as simple as saying 'eat less nuts' or 'eat more nuts' to live longer - it's about getting the protein balance right, a factor that might be particularly important for high protein diets, such as the Atkins diet or body builders' protein supplements."

Methionine is essential to the formation of all proteins. It is naturally abundant in foods such as fish and meats as well as sesame seeds, Brazil nuts and wheat germ.

Humans have around four times more genes than the fruit fly, but both share many similar genes with basic biological functions.

Therefore, even though the fruit fly does not on the surface resemble humans, many findings about its basic biology can be extrapolated to humans.

"This work was done on flies but similar results have been found in mice," said Dr Piper. "If it turns it has the same effect on humans, then the message is avoid high levels of methionine."